If PAX OXY is illuminated in the environment window of the systems MFD, what does this indicate?

• A. O2 is being supplied to the pilots
• B. O2 is being supplied to the passengers in the cabin
• C. O2 is not available
• D. O2 is being supplied to both pilots and passengers

Answer: (B)

The PAX OXY indicator on the environment window shows which oxygen circuit is currently active. When this light is illuminated, it means passenger oxygen is being supplied to the cabin. The crew may have their own indicator (CREW OXY) that would show if pilots are also receiving oxygen. If only the passenger indicator is on, oxygen is flowing to the cabin for passengers, not necessarily to the pilots. If oxygen weren’t available, that light wouldn’t be lit, or a fault message would appear.